1. Field of the Invention
The present invention relates to an exhaust gas recirculation control apparatus for an internal combustion engine and, more particularly, to an exhaust gas recirculation control apparatus for an engine having a turbocharger.
2. Description of the Related Art
In the present situation where more restrictive regulations against harmful material exhausted from an internal combustion engine have been advanced in many places from the viewpoint of an environmental protection, as a method of reducing the harmful matters contained in an exhaust gas of the internal combustion engine, exhaust gas recirculation (EGR) has been widely known and used. It has the following operation. A portion of an exhaust gas exhausted from a combustion chamber is recirculated from an exhaust manifold to an intake manifold and mixed with intake air, and the mixture is again supplied to the combustion chamber, so that the concentration of oxygen in the intake air is reduced and a combustion temperature is decreased. The EGR has such a large effect that the occurrence of the harmful matters contained in the exhaust gas, particularly, nitride oxide (hereinbelow, referred to as NOx) is suppressed.
FIG. 13 shows an intake and exhaust circuit diagram of an engine 14 with a turbocharger having a conventional exhaust gas recirculation circuit. The engine 14 comprises: a turbocharger 11; an intake circuit 12; an aftercooler 13; an exhaust gas recirculation circuit 15; an exhaust circuit 16; and an exhaust pressure control valve 18. Intake air compressed by a compressor 11a of the turbocharger 11 passes through the intake circuit 12, is cooled by the aftercooler 13 provided in the middle of the circuit 12, and is introduced to an engine main body 14a through an intake manifold 12a. The exhaust gas exhausted from the engine main body 14a flows into the turbocharger 11 through the exhaust circuit 16 to drive a turbine 11b, and is then exhausted. The exhaust pressure control valve 18 capable of adjusting an outlet pressure in the turbine 11b is provided at the outlet of the turbine 11b, The exhaust gas recirculation circuit 15 is branchingly connected in such a manner that one end is connected in the vicinity of an exhaust manifold 16a of the exhaust circuit 16 and the other end is connected in the vicinity of the intake manifold 12a of the intake circuit 12. The exhaust gas recirculation circuit 15 has: an EGR valve 15c whose opening area can be controlled so that the exhaust gas recirculation circuit 15 can be opened or closed; and an EGR cooler 15b for cooling the circulated exhaust gas. When the exhaust gas is circulated, the EGR valve 15c is first opened. A part of the exhaust gas is separated in the exhaust circuit 16 and cooled by the EGR cooler 15b, and after that, it is mixed with the intake air in the intake circuit 12. The mixture is introduced into the engine main body 14a. 
However, the above intake and exhaust circuit has the following problems.
(1) When the engine 14 is driven under certain conditions, for example, at a medium or high speed under high loads, the pressure in the intake manifold 12a is higher than that of the exhaust manifold 16a in some cases. Generally, the reason is that the engine is designed so that the characteristics of the turbocharger match with the frequently used driving conditions to raise the efficiency of the engine and obtain high power and low fuel economy. Because the pressure at the intake side is higher and the pressure at the exhaust side is lower, an intake and exhaust resistance serving as a loss of power becomes smaller. In this case, because the exhaust gas is not circulated, the harmful component contained in the exhaust gas cannot be reduced. The exhaust gas is circulated only under such driving conditions that the pressure in the intake manifold 12a is lower than that in the exhaust manifold 16a, for example, during driving at a low speed under low loads. Accordingly, the driving conditions where the exhaust gas recirculation circuit is operated to enable the harmful component in the exhaust gas to be reduced are restricted.
(2) When the circulation amount of the exhaust gas increases or decreases in association with a change in the opening degree of the EGR valve 15c, an intake flow rate to be introduced to the engine main body 14a is fluctuated as a result of a fluctuation in pressure in the intake manifold 12a. When the intake flow rate is fluctuated, the amount of oxygen to be used for combustion is fluctuated and a stable combustion state cannot be obtained, so that the rotational speed of the engine is varied.
In order to solve the above problem (1), as a method of raising the pressure of the exhaust manifold 16a so as to be higher than that of the intake manifold 12a, thereby realizing the circulation of the exhaust gas, there is a method of throttling the exhaust pressure control valve 18. According to this method, the exhaust pressure control valve 18 is throttled to raise the outlet pressure of the turbine 11b, so that the pressure of the exhaust manifold 16a located on the upstream of the turbine 11b is raised and, even if the engine 14 is driven at a medium speed or under medium loads, the exhaust gas can be circulated.
However, there is a limitation in the driving conditions of the engine 14 in which the circulation of the exhaust gas can be performed with such a method. When the pressure in the exhaust manifold 16a is excessively raised, the exhaust efficiency of the engine 14 decreases, so that the fuel economy is reduced. Accordingly, the pressure of the exhaust manifold 16a can be merely raised to such a degree that the deterioration in fuel economy can be permitted. Therefore, the range of the driving conditions of the engine 14 in which the circulation of the exhaust gas can be performed is wider than that of the engine having no exhaust pressure control valve 18 but it is limited to a narrow range.
According to the present invention, to solve the above problems, it is an object to provide an exhaust gas recirculation control apparatus for an internal combustion engine, in which while fuel economy is maintained and improved, an exhaust gas can be circulated under driving conditions of such a wide range from a low-speed and low-load area to a high-speed and high-load area and, further, a fluctuation in rotational speed accompanied with switching the circulation of the exhaust gas can be suppressed as much as possible.
To accomplish the above object, according to a first aspect of the present invention, there is provided an exhaust gas recirculation control apparatus for an internal combustion engine, in which between an intake circuit and an exhaust circuit, a turbocharger and an exhaust gas recirculation circuit that is openable by exhaust gas recirculation switching valves are provided, comprising: an intake and exhaust bypass circuit for connecting the downstream side of a compressor to the upstream side of a turbine of the turbocharger: and an intake and exhaust bypass valve whose opening area can be varied so that the intake and exhaust bypass circuit can be opened or closed, wherein an intake throttle valve whose opening area can be varied so that the intake circuit can be opened or closed is provided on the upstream side of the position of the intake circuit where the exhaust gas recirculation circuit is branchingly connected.
According to the first aspect of the present invention, a portion of the exhaust gas is allowed to flow into the exhaust circuit through the intake and exhaust bypass circuit, its flow rate can be simultaneously adjusted by the intake and exhaust bypass valve, and a loss of pressure can be generated in the intake circuit by the intake throttle valve. Consequently, even under such driving conditions that the circulation of the exhaust gas cannot be performed because the pressure in the intake circuit is higher than that in the exhaust circuit, the pressure in the intake manifold is reduced so as to be lower than that in the exhaust manifold, so that the exhaust gas can be circulated. Accordingly, under driving conditions of such a wide range from the low-speed and low-load area to the high-speed and high-load area, the exhaust gas recirculation circuit is operated, so that the harmful components in the exhaust gas can be reduced.
According to a second aspect of the present invention, there is provided an exhaust gas recirculation control apparatus for an internal combustion engine, in which between an intake circuit and an exhaust circuit, a turbocharger and an exhaust gas recirculation circuit that is openable by exhaust gas recirculation switching valves are provided, comprising: an intake and exhaust bypass circuit for connecting the downstream side of a compressor to the upstream side of a turbine of the turbocharger; and an intake and exhaust bypass valve whose opening area can be varied so that the intake and exhaust bypass circuit can be opened or closed, wherein a narrow portion is formed on the position of the intake circuit to which the exhaust gas recirculation circuit is branchingly connected.
According to the second aspect of the present invention, a portion of the exhaust gas is allowed to flow into the exhaust circuit through the intake and exhaust bypass circuit, its flow rate can be simultaneously adjusted by the intake and exhaust bypass valve, and a flow velocity of intake air is raised by the narrow portion of the intake circuit to enable its pressure to be partially reduced. Consequently, even under such driving conditions that the circulation of the exhaust gas cannot be performed because the pressure in the intake circuit is higher than that in the exhaust circuit, a decrease in pressure of the narrow portion is used to enable the exhaust gas to be circulated. Accordingly, under driving conditions of such a wide range from the low-speed and low-load area to the high-speed and high-load area, the exhaust gas recirculation circuit is operated, so that the harmful component in the exhaust gas can be reduced.
According to a third aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the first aspect of the present invention, a narrow portion is formed on the position of the intake circuit to which the exhaust gas recirculation circuit is branchingly connected.
According to the third aspect of the present invention, both of the characteristics of the first and second aspects of the present invention are provided. Consequently, under driving conditions of a wider range, the exhaust gas recirculation circuit is operated to enable the harmful component in the exhaust gas to be reduced.
According to a fourth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the first or third aspect of the present invention, there are provided detecting means for detecting driving conditions of the internal combustion engine containing an NOX exhaust amount; storage means for previously storing a target NOX exhaust amount for the driving conditions of the internal combustion engine; and control means for controlling the valve opening degree of each of the intake and exhaust bypass valve and the exhaust throttle valve in accordance with the driving conditions of the internal combustion engine so that the NOX exhaust amount of the internal combustion engine detected by the detecting means is equal to the target NOX exhaust amount stored by the storage means.
According to the fourth aspect of the present invention, first under driving conditions of a wide range of the internal combustion engine, the exhaust gas recirculation circuit is operated, thereby enabling the harmful component in the exhaust gas to be reduced. Further, since the valve opening degree of each of the intake and exhaust bypass valve and the intake throttle valve is controlled in correspondence to the driving conditions of the internal combustion engine, even under such use that the driving conditions of the internal combustion engine such as rotational speed and loads are changed momently, the exhaust gas recirculation circuit is operated so that the exhaust amount of NOX is approximated to a target value, so that a fine control to reduce the exhaust amount of NOX can be performed.
According to a fifth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the second aspect of the present invention, there are provided: an intake bypass circuit for bypassing the narrow portion of the intake circuit; and an intake bypass valve whose opening area can be varied so that the intake bypass circuit can be opened or closed.
According to the fifth aspect of the present invention, in addition to the second aspect of the present invention, the intake air can be introduced to the engine main body through the intake bypass circuit without being passed through the narrow portion. Consequently, when the exhaust gas can be circulated without depending on the above-mentioned operation of the narrow portion to reduce the pressure or when the circulation of the exhaust gas is not needed, the intake air is introduced to the engine main body through the intake bypass circuit, so that a decrease in engine efficiency due to the resistance at the narrow portion can be prevented. The flow rate of the intake air passing through the narrow portion can be adjusted by controlling the opening degree of the intake bypass valve, so that the intake pressure of the narrow portion can be adjusted more freely. Therefore, under the driving conditions of the internal combustion engine over a range wider than that of the third aspect of the present invention, the exhaust gas recirculation circuit is operated, so that the harmful component in the exhaust gas can be reduced.
According to a sixth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the fifth aspect of the present invention, there are provided: detecting means for detecting driving conditions of the internal combustion engine containing an NOX exhaust amount; storage means for previously storing a target NOX exhaust amount for the driving conditions of the internal combustion engine; and control means for controlling the valve opening degree of each of the intake and exhaust bypass valve and the intake throttle valve in accordance with the driving conditions of the internal combustion engine so that the NOX exhaust amount of the internal combustion engine detected by the detecting means is equal to the target NOX exhaust amount stored by the storage means.
According to the sixth aspect of the present invention, in addition to the fifth aspect of the present invention, the valve opening degree of each of the intake and exhaust bypass valve and the intake throttle valve is controlled in accordance with the driving conditions of the internal combustion engine. Therefore, under such use that the driving conditions of the internal combustion engine such as rotational speed and loads are changed momently, the exhaust gas recirculation circuit is operated so that the exhaust amount of NOX is approximated to a target value, so that a fine control to reduce the exhaust amount of NOX can be performed. The opening degree of the intake bypass valve is adjusted to enable the flow rate of the intake air passing through the narrow portion to be controlled, so that the intake air pressure of the narrow portion can be more freely adjusted. Therefore, under the driving conditions of the internal combustion engine over a range wider than that of the fourth aspect of the present invention, the exhaust gas recirculation circuit is operated to enable the harmful component in the exhaust gas to be reduced.
According to a seventh aspect of the present invention, in the exhaust gas recirculation control apparatus according to the fifth aspect of the present invention, there are provided: detecting means for detecting the driving conditions of the internal combustion engine containing an NOX exhaust amount; storage means for previously storing a target NOX exhaust amount for the driving conditions of the internal combustion engine; and control means for controlling in such a manner that when the internal combustion engine is driven at a high speed under high loads, while the intake and exhaust bypass valve is substantially closed, the opening degree of the intake bypass valve is controlled so that the NOX exhaust amount of the internal combustion engine detected by the detecting means is equal to the target NOX exhaust amount stored by the storage means and, when the internal combustion engine is driven at a medium speed under high loads, while the intake and exhaust bypass valve is substantially completely opened, the intake bypass valve is substantially closed.
According to the seventh aspect of the present invention, in addition to the fifth aspect of the present invention, during driving at a high speed under high loads during which the intake flow rate is large, the operation of the narrow portion is remarkably shown, and the exhaust gas can be circulated without no flow in the intake and exhaust bypass, since the intake and exhaust bypass valve is closed, a reduction in charging efficiency of the intake air caused by the intake and exhaust bypass flow can be suppressed. Therefore, the fuel economy during driving of the internal combustion engine at a high speed is improved. During driving at a medium speed under high loads during which the intake flow rate is reduced and the operation of the narrow portion is deteriorated, the intake bypass valve is substantially closed, the total amount of the intake flow is supplied to the narrow portion to reduce the pressure of the narrow portion, and simultaneously, the intake and exhaust bypass valve is opened as much as possible to reduce the pressure in the intake circuit, so that the synergistic effect is derived. Therefore, the EGR rate is raised to the maximum value and the NOX exhaust amount is suppressed to the minimum value.
According to an eighth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the first or third aspect of the present invention, there are provided: detecting means for detecting the driving conditions of the internal combustion engine containing the EGR rate; storage means for previously storing a target EGR rate for the driving conditions of the internal combustion engine; and control means for controlling the valve opening degree of each of the intake and exhaust bypass valve and the intake throttle valve in accordance with the driving conditions of the internal combustion engine so that the EGR rate of the internal combustion engine detected by the detecting means is equal to the target EGR rate stored by the storage means.
According to the eighth aspect of the present invention, under the driving conditions over a wide area of the internal combustion engine, the exhaust gas recirculation circuit is operated to enable the harmful component in the exhaust gas to be reduced. In addition, the valve opening degree of each of the intake and exhaust bypass valve and the intake throttle valve is controlled in correspondence to the driving conditions of the internal combustion engine. Therefore, even under such use that the driving conditions of the internal combustion engine such as rotational speed and loads are changed momently, the exhaust gas recirculation circuit is operated so that the exhaust amount of NOX is approximated to the target value by approximating the EGR rate to the target value, so that a fine control to reduce the exhaust amount of NOX can be performed. Further, the EGR rate is used as a controlled variable instead of the NOX exhaust amount, so that the expensive NOX detecting device is not needed and the cost can be reduced.
According to a ninth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the fifth aspect of the present invention, there are provided: detecting means for detecting the driving conditions of the internal combustion engine containing the EGR rate; storage means for previously storing a target EGR rate for the driving conditions of the internal combustion engine; and control means for controlling the valve opening degree of each of the intake and exhaust bypass valve and the intake bypass valve in accordance with the driving conditions of the internal combustion engine so that the EGR rate of the internal combustion engine detected by the detecting means is equal to the target EGR rate stored by the storage means.
According to the ninth aspect of the present invention, in addition to such a fact that the exhaust gas recirculation circuit is operated under the driving conditions over a wide range of the internal combustion engine to enable the harmful component in the exhaust gas to be reduced, the valve opening degree of each of the intake and exhaust bypass valve and the intake bypass valve is controlled in correspondence to the driving conditions of the internal combustion engine. Accordingly, even under such use that the driving conditions of the internal combustion engine such as rotational speed and loads are changed momently, the exhaust gas recirculation circuit is operated so that the exhaust amount of NOX is approximated to the target value by approximating the EGR rate to the target value, so that a fine control to reduce the exhaust amount of NOX can be performed. Further, the EGR rate is used as a controlled variable instead of the NOX exhaust amount, so that the expensive NOX detecting device is not needed and the cost can be reduced. The flow rate of the intake air passing through the narrow portion can be adjusted by controlling the opening degree of the intake bypass valve, so that the intake pressure of the narrow portion can be more freely adjusted. Therefore, the exhaust gas recirculation circuit is operated under the driving conditions of the internal combustion engine over a range wider than that of the eighth aspect of the present invention, so that the harmful component in the exhaust gas can be reduced.
According to a tenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the fifth aspect of the present invention, there are provided: detecting means for detecting driving conditions of the internal combustion engine containing the EGR rate; storage means for previously storing a target EGR rate for the driving conditions of the internal combustion engine; and control means for controlling in such a manner that when the internal combustion engine is driven at a high speed under high loads, while the intake and exhaust bypass valve is substantially closed, the opening degree of the intake bypass valve is controlled so that the EGR rate of the internal combustion engine detected by the detecting means is equal to the target EGR rate and, when the internal combustion engine is driven at a medium speed under high loads, while the intake and exhaust bypass valve is substantially completely opened, the intake bypass valve is substantially closed.
According to the tenth aspect of the present invention, in addition to the fifth aspect of the present invention, during the driving at a high speed under high loads during which the intake flow rate is large, the effect of the narrow portion remarkably appears, and even if there is no flow in the intake and exhaust bypass, the circulation of the exhaust gas can be performed only by the above-mentioned effect of the narrow portion to reduce the pressure, the intake and exhaust bypass valve is closed, so that a reduction in charging efficiency of the intake air caused by the intake and exhaust bypass flow can be suppressed. Consequently, the fuel economy of the internal combustion engine during the driving at a high speed is improved. During the driving at a medium speed under high loads during which the intake flow rate is decreased and the effect of the narrow portion is deteriorated, the intake bypass valve is substantially closed and the total amount of the intake flow is supplied to the narrow portion to reduce the pressure in the narrow portion and, simultaneously, the intake and exhaust bypass valve is opened as much as possible to reduce the pressure in the intake circuit, so that the synergistic effect can be derived. Consequently, the EGR rate is raised to the maximum value and the NOX exhaust amount is suppressed to the minimum value. Further, the EGR rate is used as a controlled variable instead of the NOX exhaust amount, so that the expensive NOX detecting device is not needed and the cost can be reduced.
According to an eleventh aspect of the present invention, in the exhaust gas recirculation control apparatus of the present invention according to any one of the first to third, fifth to seventh, ninth, and tenth aspects, there are provided: a turbine bypass circuit for connecting the upstream side to the downstream side of the turbine of the turbocharger; and a waste gate valve which is opened to open the turbine bypass circuit when the pressure of an exhaust gas on the upstream side of the turbine is equal to or larger than a predetermined value.
According to the eleventh aspect of the present invention, in addition to any one of the first to tenth aspects of the present invention, the turbine bypass circuit for connecting the upstream side to the downstream side of the turbine of the turbocharger is provided. When the exhaust pressure on the upstream side of the turbine is equal to or larger than a predetermined value, the exhaust gas is let off from the turbine bypass circuit to the downstream side of the turbine. Consequently, a reduction in exhaust efficiency caused by an excessive rise in exhaust pressure on the turbine upstream side can be prevented and the fuel economy is improved.
According to a twelfth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the first, second, third, or fifth aspect of the present invention, the intake and exhaust bypass valve is formed between the downstream side of the compressor, upstream side of the turbine, and exhaust gas recirculation circuit, this valve is a three-way valve having a switching position where a port on the downstream side of the compressor is closed to connect the upstream side of the turbine to the exhaust gas recirculation circuit and a switching position where a port on the exhaust gas recirculation circuit side is closed to connect the downstream side of the compressor to the upstream side of the turbine, and an EGR cooler for cooling the exhaust gas is provided on the position of the exhaust gas recirculation circuit located on the more upstream side than a position where exhaust gas from the three-way valve joins.
According to the twelfth aspect of the present invention, there are formed two flows of the exhaust circulation such as exhaust flow directly circulated from the exhaust gas recirculation circuit and exhaust flow circulated through the three-way valve. The exhaust gas directly recirculated from the exhaust gas circulation circuit is cooled by the EGR cooler and the exhaust gas circulated through the three-way valve is not cooled. On the basis of such a fact, a ratio of the flow rates of the two exhaust circulation flows is adjusted, so that a temperature of the exhaust gas to be circulated to the intake circuit can be controlled. Consequently, improving the combustion state can reduce the exhausted harmful matter. Simultaneously, the exhaust flow rate passing through the EGR cooler is suppressed, so that the amount of heat to be absorbed from the EGR cooler to the car body can be minimized. Consequently, improving the heat balance can reduce burdens on the cooling system.
According to a thirteenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the twelfth aspect of the present invention, during starting warming-up and driving under low loads of the internal combustion engine, the three-way valve closes the port on the downstream side of the compressor to connect the upstream side of the turbine to the exhaust gas recirculation circuit and, during the other driving conditions of the internal combustion engine, the three-way valve closes the port on the exhaust gas recirculation circuit side to connect the downstream side of the compressor to the upstream side of the turbine.
According to the thirteenth aspect of the present invention, in addition to the twelfth aspect of the present invention, during starting warming-up and driving under low loads of the internal combustion engine, the three-way valve closes the port on the downstream side of the compressor to connect the upstream side of the turbine to the exhaust gas recirculation circuit, so that the exhaust gas which does not pass through the EGR cooler is circulated, the temperature of the whole circulated exhaust gas is raised, and the warming-up time is reduced. Since warming-up is performed more quickly, white smoke (its main component is hydrocarbon) generated during starting at a low temperature is reduced. In addition, the occurrence of condensate caused by overcooling the exhaust gas through the EGR cooler during driving under low loads can be prevented and, further, the exhaust flow rate passing through the EGR cooler is suppressed, so that the amount of heat to be absorbed from the EGR cooler to the car body can be minimized. Improving the heat balance can reduce the burdens on the cooling system.
According to a fourteenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the first, second, third, or fifth aspect of the present invention, the intake and exhaust bypass valve is a check valve for permitting only flow of one direction from the downstream side of the compressor to the upstream side of the turbine.
According to the fourteenth aspect of the present invention, since the control for the flow direction of the intake and exhaust bypass circuit can be performed by the simple construction such as a check valve, the cost is reduced.
According to a fifteenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the fourteenth aspect of the present invention, the intake and exhaust bypass circuit for connecting the downstream side of the compressor to the upstream side of the turbine of the turbocharger is provided between a compressor housing and a turbine housing of the turbocharger.
According to the fifteenth aspect of the present invention, in addition to the eleventh aspect of the present invention, since the pipe of the intake and exhaust bypass circuit is directly connected to the housing of the turbocharger, the intake and exhaust bypass circuit is assembled integrally with the turbocharger, so that the assembling and maintenance are improved. Since the pipe is shortened and the intake air easily flows into the exhaust circuit, the responsibility of the intake and exhaust bypass circuit is improved and the effect on reduction in pressure of the intake circuit is remarkably shown, so that the exhausted harmful matter is further reduced.
According to a sixteenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal engine according to any one of the first to third, fifth to seventh, ninth, and tenth aspects of the present invention, the exhaust passage from the exhaust manifold of the internal combustion engine to the inlet of the turbine housing of the turbocharger is divided into a plurality of passages, and both of the exhaust gas recirculation circuit and the intake and exhaust bypass circuit are connected to at least one of the divided exhaust passages.
According to the sixteenth aspect of the present invention, in addition to the foregoing aspects of the present invention, a deterioration in exhaust efficiency due to exhaust interference between the cylinders can be prevented by dividing the exhaust passage. Only either one of the exhaust gas recirculation circuit and the intake and exhaust bypass circuit is not connected to arbitrary one of the divided exhaust passages. In other words, both of the exhaust gas recirculation circuit and the intake and exhaust bypass circuit are connected to the divided exhaust passage or both of them are not connected to it. If the exhaust gas recirculation circuit and the intake and exhaust bypass circuit are connected to the divided different exhaust passages, respectively, the connecting position is away from the other position, so that such an effect that the pressure of the exhaust gas is raised by the intake and exhaust bypass and the exhaust gas is easily circulated is deteriorated. According to the present invention, however, such a phenomenon can be prevented.
Further, since the flow rate of the exhaust gas discharged to the exhaust gas recirculation circuit is substantially equal to that of the exhaust gas supplied from the intake and exhaust bypass circuit, the flow rates of the exhaust gas sent from the divided exhaust passages to the turbine of the turbocharger denote substantially the same value. Consequently, also in the case of the divided exhaust passages, the circulation of the exhaust gas can be performed by the operation of the intake and exhaust bypass circuit and a reduction in efficiency of the turbocharger due to unbalance of the exhaust flow rates of the passages is avoided, so that a deterioration in fuel economy can be prevented.
According to a seventeenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the sixteenth aspect of the present invention, the position of the exhaust passage to which the exhaust gas recirculation circuit is connected is located on the upstream side of a position where the intake and exhaust bypass circuit is connected to the passage.
According to the seventeenth aspect of the present invention, in addition to the sixteenth aspect of the present invention, in arbitrary one of the divided exhaust passages, the connecting position of the exhaust gas recirculation circuit is located on the upstream side of the connecting position of the intake and exhaust bypass circuit. Accordingly, such a phenomenon that a part of the intake air introduced from the intake and exhaust bypass circuit to the exhaust passage is returned to the intake circuit through the exhaust gas recirculation circuit can be prevented. Therefore, such a possibility that the operation to reduce the harmful matter in the exhaust gas is damaged by mixing the intake air to the exhaust gas recirculation circuit is eliminated.
According to an eighteenth aspect of the present invention, there is provided an exhaust gas recirculation control apparatus for an internal combustion engine, in which between an intake circuit and an exhaust circuit, a turbocharger and an exhaust gas recirculation circuit that is openable by exhaust gas recirculation switching valves are provided, comprising: a turbine bypass circuit for connecting the upstream side to the downstream side of the turbine of the turbocharger; a waste gate valve which can open or close said turbine bypass circuit and whose opening degree can be controlled; and control means for controlling the valve opening degree of the waste gate valve in accordance with the driving conditions of the internal combustion engine and the EGR rate.
According to a nineteenth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the eighteenth aspect of the present invention, there are provided: detecting means for detecting driving conditions of the internal combustion engine; detecting means for detecting the EGR rate; detecting means for detecting an intake flow rate; and storage means for previously storing a target intake flow rate for the driving conditions of the internal combustion state and the EGR rate, and the control for the waste gate valve by the control means is a control to adjust the valve opening degree of the waste gate valve so that a difference between the detected intake flow rate and the target intake flow rate stored by the storage means is equal to or less than a predetermined value.
According to the eighteenth aspect of the present invention, the control means controls the valve opening degree of the waste gate valve to control the rotational speed of the turbocharger, so that the intake flow rate can be adjusted. Further, according to the nineteenth aspect of the present invention, when the circulation amount of the exhaust gas is fluctuated, the intake flow rate is adjusted to enable the flow rate of fresh air introduced to the engine main body (namely, only the fresh intake flow rate except for the circulation amount of the exhaust gas) to be held substantially constant, so that a fluctuation in amount of combustible fresh air for combustion can be suppressed. Consequently, there is no fluctuation in rotational speed of the engine and smoother driving can be realized.
According to a twentieth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the eighteenth or nineteenth aspect of the present invention, there are provided: an intake and exhaust bypass circuit for connecting the downstream side of the compressor to the upstream side of the turbine of the turbocharger; and an intake and exhaust bypass valve whose opening area can be varied so that the intake and exhaust bypass circuit can be opened or closed.
According to the twentieth aspect of the present invention, in addition to the eighteenth or nineteenth aspect of the present invention, a part of the intake air is allowed to flow into the exhaust circuit through the intake and exhaust bypass circuit to raise the pressure in the exhaust manifold and, simultaneously, the valve opening degree of the waste gate valve is controlled to adjust the intake flow rate and reduce the pressure in the intake manifold. Consequently, even under such driving conditions that since the pressure in the intake circuit is higher than that in the exhaust circuit, the circulation of the exhaust gas cannot be performed, the pressure in the intake manifold is reduced so as to be lower than that in the exhaust manifold, so that the circulation of the exhaust gas can be performed. Therefore, under the driving conditions of a wide range from a low-speed and low-load area to a high-speed and high-load area, the exhaust gas recirculation circuit is operated and the harmful component in the exhaust gas can be reduced.
Further, since the valve opening degree of the intake and exhaust bypass valve can be controlled in correspondence to the driving conditions of the internal combustion engine, even under such use that the driving conditions of the internal combustion engine such as rotational speed and loads are changed momently, the exhaust gas recirculation circuit is controlled so that the exhaust amount of NOX is approximate to a target value, so that a fine control to reduce the exhaust amount of NOX can be performed.
According to a twenty-first aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the eighteenth or nineteenth aspect of the present invention, there are provided: an intake and exhaust bypass circuit for connecting the downstream side of the compressor to the upstream side of the turbine of the turbocharger; and a check valve for permitting the flow in the intake and exhaust bypass circuit only in one direction from the downstream side of the compressor to the upstream side of the turbine.
According to the twenty-first aspect of the present invention, in addition to the eighteenth or nineteenth aspect of the present invention, a part of the intake air is allowed to flow into the exhaust circuit through the intake and exhaust bypass circuit to raise the pressure in the exhaust manifold and, simultaneously, the valve opening degree of the waste gate valve is controlled to adjust the intake flow rate and reduce the pressure in the intake manifold. Consequently, even under such driving conditions that since the pressure in the intake circuit is higher than that in the exhaust circuit, the circulation of the exhaust gas cannot be performed, the pressure in the intake manifold is reduced so as to be lower than that in the exhaust manifold, so that the circulation of the exhaust gas can be performed. Therefore, under the driving conditions of a wide range from a low-speed and low-load area to a high-speed and high-load area, the exhaust gas recirculation circuit is operated and the harmful component in the exhaust gas can be reduced. Since the control for the flow direction control of the intake and exhaust bypass circuit can be performed by the simple construction such as a check valve, the manufacturing cost can be reduced.
According to a twenty-second aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the eighteenth or nineteenth aspect of the present invention, a narrow portion is formed on the position of the intake circuit to which the exhaust gas recirculation circuit is branchingly connected, an intake bypass circuit for bypassing the narrow portion, and an intake bypass valve whose opening area can be varied so that the intake bypass circuit can be opened or closed are provided.
According to the twenty-second aspect of the present invention, in addition to the above aspects of the present invention, the narrow portion provided for the intake circuit is combined to the intake bypass circuit to control the opening degree of the intake bypass valve, so that the pressure in the narrow portion can be reduced. The exhaust gas recirculation circuit is connected to the narrow portion to enable the recirculation of the exhaust gas even during the driving at a medium speed or a high speed in the high-load area, so that the NOX exhaust amount can be reduced while the low fuel economy is maintained.
According to a twenty-third aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the eighteenth or nineteenth aspect of the present invention, there are provided: a generator, which is provided immediately on the downstream side of the waste gate valve, for allowing the pivotably engaged turbine to be rotated due to the pressure of the exhaust gas to generate electric power; a first converter for converting the electric power generated by the generator into a chargeable state; and a battery for charging the electric power generated by the generator through the first converter.
According to the twenty-third aspect of the present invention, in addition to the above-mentioned aspects of the present invention, since the generator, first converter, and battery are provided, for example, in the driving at a high speed under low loads or decelerating, the energy of the exhaust gas passing through the waste gate valve is collected as electric energy by the generator, and the energy of the exhaust gas can be effectively used.
According to a twenty-fourth aspect of the present invention, in the exhaust gas recirculation control apparatus for the internal combustion engine according to the twenty-third aspect of the present invention, there are provided: an electric motor, which is rotated by the electric power from the battery, for promoting the driving of the turbocharger; and a second converter for converting the electric power from the battery into such a state that it can be driven and supplying the converted power to the electric motor.
According to the twenty-fourth aspect of the present invention, in addition to the twenty-third aspect of the present invention, since the second converter and electric motor are provided, for example, in the driving at a high speed under low loads or accelerating, the electric motor uses the electric energy charged in the battery to promote the turbocharger, so that the responsibility can be improved, and the supercharging pressure can be raised. Consequently, while the energy of the exhaust gas is effectively used, the improvement of accelerating properties due to a reduction in turbo lag, and a reduction in smoke and an increase in low-speed torque due to an increase in intake flow rate can be realized.